Hard disk drives utilize a magnetic recording head to read/write data from/to a spinning disk coated with a layer of magnetic material. The recording track width of the magnetic recording head is one of the factors that limits the density at which data can be stored on the disk. A smaller recording track width results in more tracks per inch (TPI) on the surface of the disk and correspondingly a higher data capacity. As magnetic recording heads decrease in size and the associated recording track widths decrease in size, the complexity of testing and evaluating magnetic recording heads increases.
A number of different measurements may be used to characterize the recording track width associated with a magnetic recording head. For example, the triple-track method uses a triple-track profile to measure a magnetic write width (MWW) using direct measurement of off-track readback signals. While the triple-track method is widely used, the measured MWW is typically narrower than the physical track footprint and therefore does not accurately reflect the final magnetic recording head performance in terms of the TPI in the hard drive. Furthermore, the measured MWW is sensitive to transition edges and curvature as well as reader resolution and off-track response. Accordingly, the MWW obtained using the triple-track method is not a preferred targeting and controlling parameter.
Another commonly used measurement is the erase-profile based magnetic track width (MTW) or magnetic erase width (MEW). This measurement involves the direct measurement of magnetic erasure. In particular, this measurement measures the recording field bubble footprint width and therefore has good correlation with the final TPI of the hard drive. However, the process of making this measurement requires a relatively long testing time and is sensitive to testing noise and/or mechanical/servo instability. Accordingly, this measurement is not suitable for high volume manufacturing.